Class B foam extinguishers are not suitable for which type of flammable liquid fire?

Class B foam extinguishers are specifically designed for fires involving flammable liquids, such as hydrocarbons (gasoline, diesel, jet fuels), which are non-polar and can be effectively smothered by the foam. The foam forms a barrier over the flammable liquid, suppressing the release of flammable vapors and cooling the fire.

Cooking oil, on the other hand, represents a different category of fire hazard. Cooking oils are usually classified as Class K fires, which are characteristic of fires involving vegetable oils, animal fats, and other cooking oils at high temperatures. Class K fires require specific extinguishing agents designed to handle the unique properties of the fuels involved, such as wet chemical agents, which can effectively cool and suppress the fire while preventing re-ignition.

Using Class B foam on cooking oil fires may be ineffective or even dangerous, as it cannot properly address the characteristics of the high-temperature cooking oils and might lead to spreading the fire instead of extinguishing it. This underscores the importance of selecting the correct type of fire extinguisher based on the specific classification of the fire involved.